I am considering building up on my fourplex. 2 additional units.

Quote from @Victor Yang:In addition, is it possible for me and my wife to gift 36k worth of equity per year of the house (under the annual exclusion limit) and therefore have none of the costs go towards the lifetime gift limit?

In addition to the interest of the loan, you'd also be paying this as well. 

What else i should ask inspection to look for in addition to below.

Stock market returns have been good and I don’t have the headaches of dealing with any additional houses or guests.

This can put a significant strain on your finances and cash flowThey also often require a large down payment themselves and may have a strict repayment schedule that can be difficult to meet, especially if there are unforeseen circumstances or delays in renting the property or generating income from itIn addition, relying on this type of loan may expose you to higher financial stress and the possibility of default if you are unable to meet your loan obligationsThe final decision depends on your overall financial situation, risk tolerance, and your ability to manage the associated costs and obligations

My last note would be to try to buy 3 or less replacement properties, it makes the exchange much easier and you avoid some additional rules.

Additionally, the contract with the wholesaler is set to expire on Monday the 27th.

Long term goal is Property  Appreciation.Brand new single family home with 3000sqft (+ additional 1200sqft unfinished basement) on a 0.25 acre lot.

Of course unless your buying defaulted notes at the get go then again as Chris mentioned this type of fee should be handled up front.. and if it new origination your making and then they go bad.. in your foreclosures you can charge the borrower these fee's when they cure or add it to you opening bid and when someone buys it at the court house you get repaid..